This invention relates to a fluorescent display panel containing a chip of semiconductor integrated circuit(IC), and more particularly to a position marker for facilitating an automatic wire bonding process.
In a fluorescent display panel containing the IC chip, anode segments and lead conductors are formed on a glass substrate. One end of each lead conductor is connected to a corresponding anode segment, and the other end of the conductor forms a lead conductor bonding pad. An insulator layer is formed on the substrate by using a thick film process so as to cover the lead conductors. The insulator layer has an aperture for exposing the surfaces of the lead conductor bonding pads.
The IC chid is mounted on the substrate such that each IC bonding pad is wire-bonded to a corresponding lead conductor bonding pad.
In an operation of a fluorescent display panel, a selected anode segment is connected to an anode voltage through an IC bonding pad and a corresponding lead conductor bonding pad. Only the selected anode segments radiate fluorescent layers formed on the segments.
An automatic wire bonding machine which is program-controlled by a host computer performs the wire bonding between the IC bonding pad to a corresponding lead conductor bonding pad. The operator of this automatic wire bonding machine monitors the wire bonding through an ITV(industrial television)display.
The tip of the bonding tool of the bonding machine is position-controlled to a design center of a lead conductor bonding pad, which is stored as a data in the control program. And there is a problem of position error of the aperture of the insulator layer. Although all the centers of the lead conductor bonding pads are within an allowable range from their design center, the position of an aperture may differ by a large amount from its design position.
Since the insulator layer is formed by using screen printing, there are a variety of factors causing position errors of the aperture. A screening sheet for printing may be slackened after a number of printings, and such slackness of a screening sheet may be different at different places of the sheet. In a recent tendency, many anode segments are formed on a large glass substrate, and large area of insulator layer are formed by a single printing. As a result, it is difficult to maintain a correct positions of the aperture on the substrate.
When the position of the aperture of the insulator layer is different by a large amount from its design position, a part or the whole body of the tip of the bonding tool, which is controlled to the design center of a lead conductor bonding pad, may be placed on the insulator layer outside of the aperture. This causes an unreliable wire bonding, and originates troubles in the bonding process and in the succeeding processes.
When the automatic wire bonding machine is controlled by a program having different position data for different anode areas, the problem caused from the position error of the insulator layers can be avoided, but this makes the control program and control itself complex.